This article presents the evaluation of water-soluble palladium nanoparticles with hydrophobic active sites that are ideal for the biphasic colloidal catalysis of water-insoluble organic substrates in aqueous solution. Palladium nanoparticles stabilized with ω-carboxylate-functionalized alkanethiolate are first synthesized using ω-carboxylate-S-alkylthiosulfate as their ligand precursor. The biphasic catalysis is carried out for the reaction of hydrophobic allylic alcohols without using any additional mixing solvent or surfactant, which results in the complete consumption of substrates under the atmospheric pressure of H2 gas and at room temperature in less than 24 h. Systematic investigations on the influence of pH and substrate size are also performed to examine the utility of these thiolate-capped palladium nanoparticles as structurally stable and water-soluble micellar catalysts for the biphasic reaction.

The formation of interparticle duplex DNA conjugates with gold nanoparticles constitutes the basis for interparticle plasmonic coupling responsible for surface-enhanced Raman scattering signal amplification, but understanding of its correlation with interparticle spatial properties and particle sizes, especially in aqueous solutions, remains elusive. This report describes findings of an investigation of interparticle plasmonic coupling based on experimental measurements of localized surface plasmon resonance and surface enhanced Raman scattering characteristics for gold nanoparticles in aqueous solutions upon introduction of interparticle duplex DNA conjugates to define the interparticle spatial properties. Theoretical simulations of the interparticle optical properties and electric field enhancement based on a dimer model have also been performed to aid the understanding of the experimental results. The results have revealed a 'squeezed' interparticle spatial characteristic in which the duplex DNA-defined distance is close or shorter than A-form DNA conformation, which are discussed in terms of the interparticle interactions, providing fresh insight into the interparticle double-stranded DNA-defined interparticle spatial properties for the design of highly-sensitive nanoprobes in solutions for biomolecular detection.

Surface-enhanced Raman scattering (SERS) of plasmonic nanoparticles enables their use as nanoprobes for the detection of biomolecules in solutions, which exploits the “hot-spot” arisen from small aggregates of the biomolecule-linked nanoprobes for effective harnessing of the interparticle plasmonic coupling of gold nanoparticles. While a “squeezed” interparticle spatial characteristic has been revealed from the duplex DNA-linked gold nanoparticles as dimers in solution, how this interparticle spatial characteristic is operative for plasmonic nanoparticles containing magnetic components remains unknown. We describe herein new findings of an investigation of the interparticle spatial characteristics of DNA-linked core–shell type nanoparticles consisting of magnetic cores and plasmonic gold or silver shells, focusing on theoretical–experimental correlation in terms of localized surface plasmon resonance and electromagnetic field enhancement. While the simulated enhancement for the DNA-linked dimers of plasmonic magnetic core–gold shell nanoprobes shows an agreement with the experimental data in terms of the squeezed interparticle spacing characteristic, it does not seem to show an agreement between the simulated and experimental results for the dimers involving magnetic core–silver shell nanoprobes. Instead, an agreement was revealed by simulations of the DNA-linked dimers of the nanoprobes at an interparticle spacing of essentially zero. This finding was analyzed in terms of effective thickness of DNA layers on the nanoparticles and the strong magnetic attraction for the core–shell nanoprobes, providing new insight into the control of core composition and shell structure in optimizing the plasmonic coupling and spectroscopic enhancements for SERS-based biomolecular detection.

The role of nematic fluctuations in the pairing mechanism of iron-based superconductors is frequently debated. Here we present a novel method to reveal such fluctuations by identifying energy and momentum of the corresponding nematic boson through the detection of a boson-assisted resonant amplification of Friedel oscillations. Using Fourier-transform scanning tunneling spectroscopy, we observe for the unconventional superconductor LiFeAs strong signatures of bosonic states at momentum q ∼ 0 and energy Ω ≈ 8 meV. We show that these bosonic states survive in the normal conducting state, and, moreover, that they are in perfect agreement with well-known strong above-gap anomalies in the tunneling spectra. Attributing these small-q boson modes to nematic fluctuations we provide the first spectroscopic approach to the nematic boson in an unconventional superconductor.arXiv:1811.03489v1 [cond-mat.str-el]

Molecular anchoring and electronic properties of macrocyclic complexes fixed on gold surfaces have been investigated mainly by using scanning tunnelling microscopy (STM) and complemented with X-ray photoelectron spectroscopy (XPS). Exchange-coupled macrocyclic complexes [Ni2L(Hmba)](+) were deposited via 4-mercaptobenzoate ligands on the surface of a Au(111) single crystal from a mM solution of the perchlorate salt [Ni2L(Hmba)]ClO4 in dichloromethane. The combined results from STM and XPS show the formation of large monolayers anchored via Au-S bonds with a height of about 1.5 nm. Two apparent granular structures are visible: one related to the dinickel molecular complexes (cationic structures) and a second one related to the counterions ClO4(-) which stabilize the monolayer. No type of short and long-range order is observed. STM tip-interaction with the monolayer reveals higher degradation after 8 h of measurement. Spectroscopy measurements suggest a gap of about 2.5 eV between HOMO and LUMO of the cationic structures and smaller gap in the areas related to the anionic structures.